Contemporary radio frequency (RF) power amplifiers lack the dynamic output level control, efficiency, and linearity to meet present and future RF system requirements. Present technology RF power amplifiers utilize an analog Automatic Level Control (ALC) to control RF power output levels. These current designs have limited dynamic control range and less than desired output level stability in applications such as amplitude modulation (AM), frequency modulation (FM), spread spectrum, and special modulation waveform signals. One prior art RF power amplifier control methodology is to shift the active element's bias or operational “Q” point, which changes the gain of one or more amplifier stages, thus controlling the RF output of the power amplifier. Shifting the “Q” point degrades amplifier efficiency and linearity. This degradation is not acceptable in many systems.
Operational amplifiers are well known and were originally used to perform mathematical functions such as addition, sign changing, integration and differentiation in analog computers. Today they are used in many applications. The fundamental theories developed for analog computer modeling required the basic amplifiers to have gains of 60 dB to 140 dB. Once an amplifier met this criterion, simple mathematical formulas were used to describe operational conditions and feedback loops. This includes applications with complex impedance elements that provided integration and differentiation functions, as well as multi-pole filters. The basic theory of operational amplifiers and their applications are well understood because of their use in analog computers.
An operational amplifier contains many individual circuits within the physical package. This combination of circuits is analyzed as a composite element for operational amplifier applications. Operational amplifier circuit or application designs focus on the external feedback loops from input to output and disregard the internal circuits of the packaged amplifier. Applying the same operational amplifier feedback theory to RF power amplifiers has not been practical because the basic operational amplifier criterion of high gain is rarely met in RF amplifiers and because of the presence of parasitic impedance parameters in the feedback loop, which restrict the operational bandwidth of the amplifier. Most contemporary RF amplifiers operate over a wide RF spectrum which generally causes parasitic complex impedances throughout the amplifier circuits. The parasitic parameters may cause undesired performance over the frequency range of the RF amplifier. Some contemporary RF amplifiers utilize degenerative or negative feedback to stabilize individual RF amplifier circuits within the amplifier, but rarely interact between stages. For these or other reasons, most prior art RF amplifier designs do not provide the dynamic output level control, efficiency and linearity over a wide frequency ranges as required in new high performance applications.